1. Field
This invention relates to a method and apparatus for measuring the coefficient of rolling friction or “speed” of a surface over which a spherical projectile is rolled such as would be encountered in the game of golf on the putting green. In particular, the present invention pertains to an electronic measurement of the relative speed of the surface by sensing the time to come to rest after the ball is launched at a known initial velocity.
2. Prior Art
It is well known that putting is an integral and critical part in playing the game of golf. Being able to judge the amount of force required to propel the golf ball the exact distance to reach the target hole is extremely important to successful putting and being able to post the best possible score. This amount of force required is determined by the distance to be traversed and the effective coefficient of rolling friction of the putting green surface. This is referred to as the “speed” of the green and is affected by many factors such as the length and condition of the grass and the moisture content.
A device for measuring the speed of a putting green was developed by Edward Stimpson in 1937. This instrument which has become known as a stimpmeter consists of a ramp which releases a ball from a specific height at a predetermined angle from the horizontal. This effectively launches the ball across the green surface at a constant initial velocity. The distance that the ball rolls before coming to rest is proportional to the coefficient of rolling friction or the speed of the green. The length of the Stimpmeter from the ball release position to the release end is 30 inches. The ball is released when the ramp has been elevated to an angle of 20 degrees. The amount of kinetic energy imparted to the ball therefore results in an initial velocity of approximately 95 inches per second as the ball leaves the ramp. The distance, measured in feet, that the ball rolls across the green given this velocity has been defined as the “stimp value” of the green. The stimpmeter has been designated by the U.S. Golf Association as the recognized standard for measuring and categorizing putting green speeds. This distance may vary between approximately 6 feet for a very slow green to 14 feet for a fast green. This system of measurement has become the de-facto standard for classifying the speed of a putting green.
Although there have been some incremental improvements in this measurement device over the years, the basic method has not changed since its inception some seventy years ago. A similar apparatus was developed by David Pelz as described in U.S. Pat. No. 6,860,139. Pelz's contribution to the art was to design a precision version of the original stimpmeter that eliminated some of the variables that could contribute to inconsistencies in the reading, such as instability in holding the ramp steady during the release and variations in the exact height of the ball at the time of release. Another device disclosed by Marchese in U.S. Pat. No. 6,547,680 is basically a replica of the original stimpmeter with a few embellishments. Other prior art includes U.S. Pat. No. 6,749,527 to Hughes. This invention is a scaled down, collapsible version of the stimpmeter ramp. One common characteristic of these prior art methods is the requirement that a physical distance measurement be taken to determine the length of the path that the ball has rolled after being released from the device. This action is relatively time consuming and inconvenient for frequent or casual use in the characterization of putting surfaces. An electronic apparatus which does not require a measurement of the distance rolled is disclosed in U.S. Pat. No. 7,306,524 to Rogers. The change in velocity or deceleration that occurs between two points on the surface to be measured is used to calculate the speed of the green. This device is relatively large and bulky and not well suited to casual or frequent use on the course.
All of the devices and methods heretofore known suffer from one or more disadvantages when compared to the present invention:
(a) A physical measurement of the distance rolled by the measuring ball across the green must be performed by the operator using a tape measure or similar instrument. This action is relatively time consuming and inconvenient to complete.
(b) The devices are too large to be routinely carried for repeated and frequent use throughout the course of play.